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Commit eaa2f87c authored by Dan Carpenter's avatar Dan Carpenter Committed by Ingo Molnar
Browse files

x86/ldt: Fix off by one in get_segment_base() 



ldt->entries[] is allocated in alloc_ldt_struct().  It has
ldt->nr_entries elements and ldt->nr_entries is capped at LDT_ENTRIES.
So if "idx" is == ldt->nr_entries then we're reading beyond the end of
the buffer.  It seems duplicative to have two limit checks when one
would work just as well so I removed the check against LDT_ENTRIES.

The gdt_page.gdt[] array has GDT_ENTRIES entries.

Signed-off-by: default avatarDan Carpenter <dan.carpenter@oracle.com>
Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-janitors@vger.kernel.org
Fixes: d07bdfd3 ("perf/x86: Fix USER/KERNEL tagging of samples properly")
Link: http://lkml.kernel.org/r/20170818102516.gqwm4xdvvuvjw5ho@mwanda


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 9c3a815f

arch/x86/events/core.c

+2 −5
Original line number Diff line number Diff line
@@ -2335,12 +2335,9 @@ static unsigned long get_segment_base(unsigned int segment) 
#ifdef CONFIG_MODIFY_LDT_SYSCALL

		struct ldt_struct *ldt;



		if (idx > LDT_ENTRIES)

			return 0;



		/* IRQs are off, so this synchronizes with smp_store_release */

		ldt = lockless_dereference(current->active_mm->context.ldt);

		if (!ldt || idx > ldt->nr_entries)

		if (!ldt || idx >= ldt->nr_entries)

			return 0;



		desc = &ldt->entries[idx];
@@ -2348,7 +2345,7 @@ static unsigned long get_segment_base(unsigned int segment) 
		return 0;

#endif

	} else {

		if (idx > GDT_ENTRIES)

		if (idx >= GDT_ENTRIES)

			return 0;



		desc = raw_cpu_ptr(gdt_page.gdt) + idx;